MysqlReplicationReporter.php
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MysqlReplicationReporter.php
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	<?php
	/**
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License as published by
	* the Free Software Foundation; either version 2 of the License, or
	* (at your option) any later version.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License along
	* with this program; if not, write to the Free Software Foundation, Inc.,
	* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
	* http://www.gnu.org/copyleft/gpl.html
	*
	* @file
	*/
	namespace Wikimedia\Rdbms\Replication;

	use InvalidArgumentException;
	use RuntimeException;
	use stdClass;
	use Wikimedia\Rdbms\DBPrimaryPos;
	use Wikimedia\Rdbms\DBQueryError;
	use Wikimedia\Rdbms\IDatabase;
	use Wikimedia\Rdbms\MySQLPrimaryPos;
	use Wikimedia\Rdbms\Platform\ISQLPlatform;
	use Wikimedia\Rdbms\Query;

	/**
	* @internal
	* @ingroup Database
	* @since 1.40
	*/
	class MysqlReplicationReporter extends ReplicationReporter {
	/** @var MySQLPrimaryPos */
	protected $lastKnownReplicaPos;
	/** @var string Method to detect replica DB lag */
	protected $lagDetectionMethod;
	/** @var array Method to detect replica DB lag */
	protected $lagDetectionOptions = [];
	/** @var bool bool Whether to use GTID methods */
	protected $useGTIDs = false;
	/** @var stdClass\|null */
	private $replicationInfoRow;
	// Cache getServerId() for 24 hours
	private const SERVER_ID_CACHE_TTL = 86400;

	/** @var float Warn if lag estimates are made for transactions older than this many seconds */
	private const LAG_STALE_WARN_THRESHOLD = 0.100;

	public function __construct(
	$topologyRole,
	$logger,
	$srvCache,
	$lagDetectionMethod,
	$lagDetectionOptions,
	$useGTIDs
	) {
	parent::__construct( $topologyRole, $logger, $srvCache );
	$this->lagDetectionMethod = $lagDetectionMethod;
	$this->lagDetectionOptions = $lagDetectionOptions;
	$this->useGTIDs = $useGTIDs;
	}

	protected function doGetLag( IDatabase $conn ) {
	if ( $this->lagDetectionMethod === 'pt-heartbeat' ) {
	return $this->getLagFromPtHeartbeat( $conn );
	} else {
	return $this->getLagFromSlaveStatus( $conn );
	}
	}

	/**
	* @param IDatabase $conn To make queries
	* @return int\|false Second of lag
	*/
	protected function getLagFromSlaveStatus( IDatabase $conn ) {
	$query = new Query(
	'SHOW SLAVE STATUS',
	ISQLPlatform::QUERY_SILENCE_ERRORS \| ISQLPlatform::QUERY_IGNORE_DBO_TRX \| ISQLPlatform::QUERY_CHANGE_NONE,
	'SHOW',
	null,
	'SHOW SLAVE STATUS'
	);
	$res = $conn->query( $query, __METHOD__ );
	$row = $res ? $res->fetchObject() : false;
	// If the server is not replicating, there will be no row
	if ( $row && strval( $row->Seconds_Behind_Master ) !== '' ) {
	// https://mariadb.com/kb/en/delayed-replication/
	// https://dev.mysql.com/doc/refman/5.6/en/replication-delayed.html
	return intval( $row->Seconds_Behind_Master + ( $row->SQL_Remaining_Delay ?? 0 ) );
	}

	return false;
	}

	/**
	* @param IDatabase $conn To make queries
	* @return float\|false Seconds of lag
	*/
	protected function getLagFromPtHeartbeat( IDatabase $conn ) {
	$currentTrxInfo = $this->getRecordedTransactionLagStatus( $conn );
	if ( $currentTrxInfo ) {
	// There is an active transaction and the initial lag was already queried
	$staleness = microtime( true ) - $currentTrxInfo['since'];
	if ( $staleness > self::LAG_STALE_WARN_THRESHOLD ) {
	// Avoid returning higher and higher lag value due to snapshot age
	// given that the isolation level will typically be REPEATABLE-READ
	// but UTC_TIMESTAMP() is not affected by point-in-time snapshots
	$this->logger->warning(
	"Using cached lag value for {db_server} due to active transaction",
	$this->getLogContext( $conn, [
	'method' => __METHOD__,
	'age' => $staleness,
	'exception' => new RuntimeException()
	] )
	);
	}

	return $currentTrxInfo['lag'];
	}

	$ago = $this->fetchSecondsSinceHeartbeat( $conn );
	if ( $ago !== null ) {
	return max( $ago, 0.0 );
	}

	$this->logger->error(
	"Unable to find pt-heartbeat row for {db_server}",
	$this->getLogContext( $conn, [
	'method' => __METHOD__
	] )
	);

	return false;
	}

	/**
	* @param IDatabase $conn To make queries
	* @return float\|null Elapsed seconds since the newest beat or null if none was found
	* @see https://www.percona.com/doc/percona-toolkit/2.1/pt-heartbeat.html
	*/
	protected function fetchSecondsSinceHeartbeat( IDatabase $conn ) {
	// Some setups might have pt-heartbeat running on each replica server.
	// Exclude the row for events originating on this DB server. Assume that
	// there is only one active replication channel and that any other row
	// getting updates must be the row for the primary DB server.
	$where = $conn->makeList(
	$this->lagDetectionOptions['conds'] ?? [ 'server_id != @@server_id' ],
	ISQLPlatform::LIST_AND
	);
	// User mysql server time so that query time and trip time are not counted.
	// Use ORDER BY for channel based queries since that field might not be UNIQUE.
	$query = new Query(
	"SELECT TIMESTAMPDIFF(MICROSECOND,ts,UTC_TIMESTAMP(6)) AS us_ago " .
	"FROM heartbeat.heartbeat WHERE $where ORDER BY ts DESC LIMIT 1",
	ISQLPlatform::QUERY_SILENCE_ERRORS \| ISQLPlatform::QUERY_IGNORE_DBO_TRX \| ISQLPlatform::QUERY_CHANGE_NONE,
	'SELECT',
	null,
	"SELECT TIMESTAMPDIFF(MICROSECOND,ts,UTC_TIMESTAMP(6)) AS us_ago " .
	"FROM heartbeat.heartbeat WHERE ? ORDER BY ts DESC LIMIT 1",
	);
	$res = $conn->query( $query, __METHOD__ );
	$row = $res ? $res->fetchObject() : false;

	return $row ? ( $row->us_ago / 1e6 ) : null;
	}

	public function getApproximateLagStatus( IDatabase $conn ) {
	if ( $this->lagDetectionMethod === 'pt-heartbeat' ) {
	// Disable caching since this is fast enough and we don't want
	// to be too pessimistic by having both the cache TTL and the
	// pt-heartbeat interval count as lag in getSessionLagStatus()
	return parent::getApproximateLagStatus( $conn );
	}

	$key = $this->srvCache->makeGlobalKey( 'mysql-lag', $conn->getServerName() );
	$approxLag = $this->srvCache->get( $key );
	if ( !$approxLag ) {
	$approxLag = parent::getApproximateLagStatus( $conn );
	$this->srvCache->set( $key, $approxLag, 1 );
	}

	return $approxLag;
	}

	/**
	* @param IDatabase $conn To make queries
	* @param string $fname
	* @return stdClass Process cached row
	*/
	public function getReplicationSafetyInfo( IDatabase $conn, $fname ) {
	if ( $this->replicationInfoRow === null ) {
	$this->replicationInfoRow = $conn->selectRow(
	[],
	[
	'innodb_autoinc_lock_mode' => '@@innodb_autoinc_lock_mode',
	'binlog_format' => '@@binlog_format',
	],
	[],
	$fname
	);
	}
	return $this->replicationInfoRow;
	}

	/**
	* @return bool Whether GTID support is used (mockable for testing)
	*/
	protected function useGTIDs() {
	return $this->useGTIDs;
	}

	public function primaryPosWait( IDatabase $conn, DBPrimaryPos $pos, $timeout ) {
	if ( !( $pos instanceof MySQLPrimaryPos ) ) {
	throw new InvalidArgumentException( "Position not an instance of MySQLPrimaryPos" );
	}

	if ( $this->topologyRole === IDatabase::ROLE_STATIC_CLONE ) {
	$this->logger->debug(
	"Bypassed replication wait; database has a static dataset",
	$this->getLogContext( $conn, [ 'method' => __METHOD__, 'raw_pos' => $pos ] )
	);

	return 0; // this is a copy of a read-only dataset with no primary DB
	} elseif ( $this->lastKnownReplicaPos && $this->lastKnownReplicaPos->hasReached( $pos ) ) {
	$this->logger->debug(
	"Bypassed replication wait; replication known to have reached {raw_pos}",
	$this->getLogContext( $conn, [ 'method' => __METHOD__, 'raw_pos' => $pos ] )
	);

	return 0; // already reached this point for sure
	}

	// Call doQuery() directly, to avoid opening a transaction if DBO_TRX is set
	if ( $pos->getGTIDs() ) {
	// Get the GTIDs from this replica server too see the domains (channels)
	$refPos = $this->getReplicaPos( $conn );
	if ( !$refPos ) {
	$this->logger->error(
	"Could not get replication position on replica DB to compare to {raw_pos}",
	$this->getLogContext( $conn, [ 'method' => __METHOD__, 'raw_pos' => $pos ] )
	);

	return -1; // this is the primary DB itself?
	}
	// GTIDs with domains (channels) that are active and are present on the replica
	$gtidsWait = $pos::getRelevantActiveGTIDs( $pos, $refPos );
	if ( !$gtidsWait ) {
	$this->logger->error(
	"No active GTIDs in {raw_pos} share a domain with those in {current_pos}",
	$this->getLogContext( $conn, [
	'method' => __METHOD__,
	'raw_pos' => $pos,
	'current_pos' => $refPos
	] )
	);

	return -1; // $pos is from the wrong cluster?
	}
	// Wait on the GTID set
	$gtidArg = $conn->addQuotes( implode( ',', $gtidsWait ) );
	if ( strpos( $gtidArg, ':' ) !== false ) {
	// MySQL GTIDs, e.g "source_id:transaction_id"
	$query = new Query(
	"SELECT WAIT_FOR_EXECUTED_GTID_SET($gtidArg, $timeout)",
	ISQLPlatform::QUERY_IGNORE_DBO_TRX \| ISQLPlatform::QUERY_CHANGE_NONE,
	'SELECT',
	null,
	"SELECT WAIT_FOR_EXECUTED_GTID_SET(?, ?)"
	);
	} else {
	// MariaDB GTIDs, e.g."domain:server:sequence"
	$query = new Query(
	"SELECT MASTER_GTID_WAIT($gtidArg, $timeout)",
	ISQLPlatform::QUERY_IGNORE_DBO_TRX \| ISQLPlatform::QUERY_CHANGE_NONE,
	'SELECT',
	null,
	"SELECT MASTER_GTID_WAIT(?, ?)"
	);
	}
	$waitPos = implode( ',', $gtidsWait );
	} else {
	// Wait on the binlog coordinates
	$encFile = $conn->addQuotes( $pos->getLogFile() );
	// @phan-suppress-next-line PhanTypeArraySuspiciousNullable
	$encPos = intval( $pos->getLogPosition()[$pos::CORD_EVENT] );
	$query = new Query(
	"SELECT MASTER_POS_WAIT($encFile, $encPos, $timeout)",
	ISQLPlatform::QUERY_IGNORE_DBO_TRX \| ISQLPlatform::QUERY_CHANGE_NONE,
	'SELECT',
	null,
	"SELECT MASTER_POS_WAIT(?, ?, ?)"
	);
	$waitPos = $pos->__toString();
	}

	$start = microtime( true );
	$res = $conn->query( $query, __METHOD__ );
	$row = $res->fetchRow();
	$seconds = max( microtime( true ) - $start, 0 );

	// Result can be NULL (error), -1 (timeout), or 0+ per the MySQL manual
	$status = ( $row[0] !== null ) ? intval( $row[0] ) : null;
	if ( $status === null ) {
	$this->logger->error(
	"An error occurred while waiting for replication to reach {wait_pos}",
	$this->getLogContext( $conn, [
	'raw_pos' => $pos,
	'wait_pos' => $waitPos,
	'sql' => $query->getSQL(),
	'seconds_waited' => $seconds,
	'exception' => new RuntimeException()
	] )
	);
	} elseif ( $status < 0 ) {
	$this->logger->info(
	"Timed out waiting for replication to reach {wait_pos}",
	$this->getLogContext( $conn, [
	'raw_pos' => $pos,
	'wait_pos' => $waitPos,
	'timeout' => $timeout,
	'sql' => $query->getSQL(),
	'seconds_waited' => $seconds,
	] )
	);
	} elseif ( $status >= 0 ) {
	$this->logger->debug(
	"Replication has reached {wait_pos}",
	$this->getLogContext( $conn, [
	'raw_pos' => $pos,
	'wait_pos' => $waitPos,
	'seconds_waited' => $seconds,
	] )
	);
	// Remember that this position was reached to save queries next time
	$this->lastKnownReplicaPos = $pos;
	}

	return $status;
	}

	/**
	* Get the position of the primary DB from SHOW SLAVE STATUS
	*
	* @param IDatabase $conn To make queries
	* @return MySQLPrimaryPos\|false
	*/
	public function getReplicaPos( IDatabase $conn ) {
	$now = microtime( true ); // as-of-time before fetching GTID variables

	if ( $this->useGTIDs() ) {
	// Try to use GTIDs, fallbacking to binlog positions if not possible
	$data = $this->getServerGTIDs( $conn, __METHOD__ );
	// Use gtid_slave_pos for MariaDB and gtid_executed for MySQL
	foreach ( [ 'gtid_slave_pos', 'gtid_executed' ] as $name ) {
	if ( isset( $data[$name] ) && strlen( $data[$name] ) ) {
	return new MySQLPrimaryPos( $data[$name], $now );
	}
	}
	}

	$data = $this->getServerRoleStatus( $conn, 'SLAVE', __METHOD__ );
	if ( $data && strlen( $data['Relay_Master_Log_File'] ) ) {
	return new MySQLPrimaryPos(
	"{$data['Relay_Master_Log_File']}/{$data['Exec_Master_Log_Pos']}",
	$now
	);
	}

	return false;
	}

	/**
	* Get the position of the primary DB from SHOW MASTER STATUS
	*
	* @param IDatabase $conn To make queries
	* @return MySQLPrimaryPos\|false
	*/
	public function getPrimaryPos( IDatabase $conn ) {
	$now = microtime( true ); // as-of-time before fetching GTID variables

	$pos = false;
	if ( $this->useGTIDs() ) {
	// Try to use GTIDs, fallbacking to binlog positions if not possible
	$data = $this->getServerGTIDs( $conn, __METHOD__ );
	// Use gtid_binlog_pos for MariaDB and gtid_executed for MySQL
	foreach ( [ 'gtid_binlog_pos', 'gtid_executed' ] as $name ) {
	if ( isset( $data[$name] ) && strlen( $data[$name] ) ) {
	$pos = new MySQLPrimaryPos( $data[$name], $now );
	break;
	}
	}
	// Filter domains that are inactive or not relevant to the session
	if ( $pos ) {
	$pos->setActiveOriginServerId( $this->getServerId( $conn ) );
	$pos->setActiveOriginServerUUID( $this->getServerUUID( $conn ) );
	if ( isset( $data['gtid_domain_id'] ) ) {
	$pos->setActiveDomain( $data['gtid_domain_id'] );
	}
	}
	}

	if ( !$pos ) {
	$data = $this->getServerRoleStatus( $conn, 'MASTER', __METHOD__ );
	if ( $data && strlen( $data['File'] ) ) {
	$pos = new MySQLPrimaryPos( "{$data['File']}/{$data['Position']}", $now );
	}
	}

	return $pos;
	}

	/**
	* @param IDatabase $conn To make queries
	* @return string Value of server_id (32-bit integer, unique to the replication topology)
	* @throws DBQueryError
	*/
	protected function getServerId( IDatabase $conn ) {
	$fname = __METHOD__;
	return $this->srvCache->getWithSetCallback(
	$this->srvCache->makeGlobalKey( 'mysql-server-id', $conn->getServerName() ),
	self::SERVER_ID_CACHE_TTL,
	static function () use ( $conn, $fname ) {
	$query = new Query(
	"SELECT @@server_id AS id",
	ISQLPlatform::QUERY_IGNORE_DBO_TRX \| ISQLPlatform::QUERY_CHANGE_NONE,
	'SELECT',
	null,
	"SELECT @@server_id AS id"
	);
	$res = $conn->query( $query, $fname );

	return $res->fetchObject()->id;
	}
	);
	}

	/**
	* @param IDatabase $conn To make queries
	* @return string\|null Value of server_uuid (hyphenated 128-bit hex string, globally unique)
	* @throws DBQueryError
	*/
	protected function getServerUUID( IDatabase $conn ) {
	$fname = __METHOD__;
	return $this->srvCache->getWithSetCallback(
	$this->srvCache->makeGlobalKey( 'mysql-server-uuid', $conn->getServerName() ),
	self::SERVER_ID_CACHE_TTL,
	static function () use ( $conn, $fname ) {
	$query = new Query(
	"SHOW GLOBAL VARIABLES LIKE 'server_uuid'",
	ISQLPlatform::QUERY_IGNORE_DBO_TRX \| ISQLPlatform::QUERY_CHANGE_NONE,
	'SHOW',
	null,
	"SHOW GLOBAL VARIABLES LIKE 'server_uuid'"
	);
	$res = $conn->query( $query, $fname );
	$row = $res->fetchObject();

	return $row ? $row->Value : null;
	}
	);
	}

	/**
	* @param IDatabase $conn To make queries
	* @param string $fname
	* @return string[]
	*/
	protected function getServerGTIDs( IDatabase $conn, $fname ) {
	$map = [];

	$flags = ISQLPlatform::QUERY_IGNORE_DBO_TRX \| ISQLPlatform::QUERY_CHANGE_NONE;

	// Get global-only variables like gtid_executed
	$query = new Query(
	"SHOW GLOBAL VARIABLES LIKE 'gtid_%'",
	$flags,
	'SHOW',
	null,
	"SHOW GLOBAL VARIABLES LIKE 'gtid_%'"
	);
	$res = $conn->query( $query, $fname );
	foreach ( $res as $row ) {
	$map[$row->Variable_name] = $row->Value;
	}
	// Get session-specific (e.g. gtid_domain_id since that is were writes will log)
	$query = new Query(
	"SHOW SESSION VARIABLES LIKE 'gtid_%'",
	$flags,
	'SHOW',
	null,
	"SHOW SESSION VARIABLES LIKE 'gtid_%'"
	);
	$res = $conn->query( $query, $fname );
	foreach ( $res as $row ) {
	$map[$row->Variable_name] = $row->Value;
	}

	return $map;
	}

	/**
	* @param IDatabase $conn To make queries
	* @param string $role One of "MASTER"/"SLAVE"
	* @param string $fname
	* @return array<string,mixed>\|null Latest available server status row; false on failure
	*/
	protected function getServerRoleStatus( IDatabase $conn, $role, $fname ) {
	$query = new Query(
	"SHOW $role STATUS",
	ISQLPlatform::QUERY_SILENCE_ERRORS \| ISQLPlatform::QUERY_IGNORE_DBO_TRX \| ISQLPlatform::QUERY_CHANGE_NONE,
	'SHOW',
	null,
	"SHOW $role STATUS"
	);
	$res = $conn->query( $query, $fname );
	$row = $res ? $res->fetchRow() : false;

	return ( $row ?: null );
	}

	}

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